Invincibility or Invulnerability?

Invulnerability refers to the fact that the strike is dealt without any damage done. Some what similar to Infinite Endurability if I'm not mistaken. (opposite to vulnerable: easily damaged)
Invincibility proposes a sense of being out of someone's capability to deal ANY strike on to begin with (which suits the Bucc's legit hacks) therefore impossible to conquer.

Here are some references:
-

 invulnerability

# having the strength to withstand attack
# the property of being invulnerable; the property of being incapable of being hurt (physically or emotionally)
wordnetweb.princeton.edu/perl/webwn

# Vulnerability is the susceptibility to physical or emotional injury or attack. It also means to have one's guard down, open to censure or criticism; assailable. Vulnerability refers to a person's state of being liable to succumb, as to persuasion or temptation.
en.wikipedia.org/wiki/Invulnerability

# invulnerable - immune to attack; impregnable; "gunners raked the beach from invulnerable positions on the cliffs"
wordnetweb.princeton.edu/perl/webwn

# invulnerable - Incapable of being wounded, or of receiving injury; not vulnerable; Unanswerable; irrefutable; unable to be damaged by an attack or convinced; as, an invulnerable argument
en.wiktionary.org/wiki/invulnerable

-

 invincibility

# indomitability: the property being difficult or impossible to defeat
wordnetweb.princeton.edu/perl/webwn

# The quality or state of being invincible; invincibleness
en.wiktionary.org/wiki/invincibility

The definition of invincibility is somewhat vague, but I suppose it is implied that if you can't touch something, you can't dream about killing it.